Numerous types of sound suppression or attenuation devices are known in the art which, to a greater or lesser degree, accomplish the function of silencing the device to which they are attached. Although great advances have been made in this field, often the advance is offset by an increase in size of the device or in complexity, thus resulting in increased manufacturing costs. The cost problem is exacerbated because, in many such devices, the size of the components then must be precisely selected so that the device is "tuned" to its particular application. Thus, certain components of a muffler must be completely retooled to meet requirements of different engine applications.
A highly effective sound suppression apparatus employing a venturi is shown in U.S. Pat. No. 3,672,464, for a straight-through flow design and for an alternate construction, U.S. Pat. No. 4,267,899. This apparatus was further improved by the use of dual venturis in U.S. Pat. No. 4,368,799. While highly successful devices, these mufflers involved high production costs, as well as expensive tooling for necessary sizes.
It would be desirable to produce a venturi-like sound attenuating device, such as a sonic choke, which has good suppression characteristics but could be inexpensively manufactured in a variety of sizes without expensive retooling. Furthermore, it would also be desirable to achieve those same suppression characteristics in the same or smaller overall package without significant increase in backpressure.
A closely related use of venturis is in exhaust ejectors. Many engine air cleaners are typically designed so that particulate matter separated out may be continuously removed or scavenged through a source of negative pressure connected to the air cleaner, and it is known that a suitable negative pressure for this purpose can be obtained by inserting a venturi into an engine exhuast pipe and a scavenge tube into the venturi. The venturi and scavenge tube thus form an ejector which may or may not be combined with a muffler. Such an ejector arrangement is shown in U.S. Pat. No. 3,137,553, to Billey. It is also known to combine the functions of muffling and ejection into a single unit, such as is shown in U.S. Pat. No.
3,419,892, issued to Wagner et al. In the Wagner et al. disclosure, there is employed a circular venturi which has excellent backpressure and scavenge performance, but because it must be manufactured from spun or die formed parts, such a design is quite expensive to manufacture. Furthermore, even slight changes in size of the venturi require manufacture of completely new dies, making multiple sized units very expensive.
In addition, in some applications, an offset venturi is required in order to meet the space limitations. Such a venturi is shown in U.S. Pat. No. 4,325,460, issued to Hoppenstedt. This device suffers from somewhat poorer performance then the circular venturi, and requires substantially more length to produce the necessary velocity head recovery. If the backpressure and vacuum characteristics of the prior circular venturis can be maintained while reducing the cost of manufacture and perhaps the size of the device, a substantial improvement in the art would be achieved. The present invention provides such an apparatus which meets or exceeds the prior art characteristics for sound suppression and particulate ejection while providing substantial reduction in cost and, in some cases, overall dimensions of the package.